heater fan on 1995 GMC Jimmy

the heater fan does not work all the time . When it does not run it will not run at any speed. Sometimes it will run and at various speeds. It has been doing this for some time now. Bill

2 answers
sounds like your resister is going out or you have a wiring issue, check the resister first if that fixes it your good to go
We have seen the blower motors that are intermittently failing cause this as well